Laportea canadensis is a perennial herb, 0.5-1 m tall, stems armed with stinging hairs, roots fibrous, often colonial from rhizomes, associated with VA mycorrhizas (Brundrett and Kendrick 1988).
Leaves alternate, stalked, blade 8-15 cm long, broadly egg-shaped, hairy, veins palmate at base, pinnate above, deeply impressed, tip long-pointed, margin coarsely toothed.
Flowers greenish, tiny, monoecious, male flowers dense, branched, in axillary clusters, female flowers in large, dense, branched, spreading clusters in upper axils longer than leaf stalks; blooms July-Aug. (Hough 1983); wind pollinated (Lovell 1918).
Fruit dry, an achene enclosed within 2 persistent sepals; fruits Aug.-Sept. (Hough 1983).
Wetland status: FACW.
Frequency in NYC: Infrequent but often in large colonies.
Habitat: Moist woods or swamp forest edges, flood plain forests, shade tolerant.
Notes: Host to larvae of the mourning cloak butterfly, Nymphalis antiopa (native to Europe (Wright 1993)); question mark butterfly, Polygonia interrogationis, and the comma butterfly, P. comma, all family Nymphalidae (Tallamy 2003; Pyle 1981).